Known gear-type transmission apparatuses having a dual clutch are disclosed, for example, in JP2003532040A and in JP2003522922A.
As illustrated in FIG. 6, in the known gear-type transmission apparatus disclosed in JP2003532040A, two parallel gear paths are formed by a transmission input shaft 503 and a transmission input shaft 504 that is formed in a hollow shape and surrounds the transmission input shaft 503, and two transmission output shafts 505 and 506 arranged in parallel to the transmission input shafts 503 and 504. The two gear paths arranged parallel to each other are connected to a driving shaft 501 of an engine via a clutch unit 502. The clutch unit 502 includes two clutch discs 502a and 502b. The clutch disc 502a is assigned to the first transmission input shaft 503 carrying gears of a 1st gear set 506, of a 3rd gear set 209 and of a 5th gear set 511. The clutch disc 502b is assigned to the second transmission input shaft 504 carrying gears of a 2nd gear set 508, of a 4th gear set 510 and of a 6th gear set 512. Further, in the known gear-type transmission apparatus disclosed in JP2003532040, a transmission driven shaft 519, at which two reverse shift stage gears 513 and 514 for backwardly driving a vehicle are provided, is additionally provided at the transmission apparatus. The transmission input shafts 503 and 504 are assigned to the reverse shift stage gears 513 and 514 of the reverse gear set respectively.
The known gear-type transmission apparatus disclosed in JP2003532040 transmits an engine torque to the transmission output shaft 506 for a forward movement of the vehicle in a manner where, firstly each of the clutch discs 502a and 502b is engaged in turn, secondly the known gear-type transmission apparatus selects any one of the 1st shift stage gear 507, the 2nd shift stage gear 508 and the 4th shift stage gear 510 by an operation of two slide sleeves 517 and 518 in order to shift a rotational direction of each of the transmission input shaft 503 and 504 to a rotational direction for forwardly moving the vehicle and then the known gear-type transmission apparatus transmits the shifted rotation to the transmission output shaft 506, thirdly the known gear-type transmission apparatus selects anyone of the 3rd shift stage gear 509, a 5th shift stage gear 511 and a 6th shift stage gear 512 by an operation of two slide sleeves 515 and 516 in order to shift the rotational direction of each of the transmission input shafts 503 and 504 to the rotational direction for forwardly moving the vehicle, and finally the known gear-type transmission apparatus transmits the shifted rotation of each of the transmission input shafts 503 and 504 to the transmission output shaft 505. On the other hand, the known gear-type transmission apparatus disclosed in JP2003532040 transmits the engine torque to the transmission output shaft 506 for a reverse movement of the vehicle by operating the reverse gear set 513 and 514 by the operation of the slide sleeve 515 and by shifting the rotational direction of the transmission input shaft 504 to a rotational direction for backwardly moving the vehicle. As a result, the known gear-type transmission transmits the shifted rotation to the transmission output shaft 506.
On the other hand, the known gear-type transmission apparatus disclosed in JP2003522922 includes an output shaft, which is arranged at substantially centre of the gear-type transmission apparatus, and a first and a second shafts, both of which are arranged parallel to the output shaft. In the known gear-type transmission apparatus disclosed in JP2003522922, two gear paths are formed in parallel by the output shaft and the first shaft and by the output shaft and the second shaft. Each of the gear paths is connected to an engine via a clutch unit including a first and a second clutches. The first clutch is assigned to one of the gear paths having four different shift stages for forward movement, and the second clutch is assigned to the other gear path having three different shift stage gear sets for the forward movement and a reverse shift stage gear set for backwardly moving the vehicle. The reverse shift stage gear set includes three gears (a first, a second and a third gears), which are engaged with each other. Further, the second gear of the reverse shift stage gear set is provided at an intermediate shaft that is provided at the known gear-type transmission apparatus disclosed in JP2003522922 in addition to the output shaft, the first and the second shafts. The known gear-type transmission apparatus disclosed in JP2003522922 achieves each shift stage by engaging/disengaging the two clutches in turn and by operating two shift stage switching clutch devices provided at each of the first and the second shafts.
In the above-mentioned known gear-type transmission apparatuses, each shaft to which gears for the forward movement is arranged parallel to each other to be rotatable around an axial line thereof. Further, in the above-mentioned known gear-type transmission apparatus, a gear change mechanism is provided between the shaft arranged along an axial line and one of the two shafts, and another gear change mechanism is provided between the shaft arranged along the axial line and the other one of the two shafts. The two gear change mechanisms are provided so as to be in parallel to each other in the axial direction of the shafts and so as to face to each other. As a result, an entire length of the known gear-type transmission apparatuses is reduced.
However, each of the above-mentioned gear-type transmission apparatuses further includes another shaft (a reverse shaft) that supports at least one of the gears for reverse movement in addition to the three shafts and that provided in parallel to the axial lines thereof. Therefore, a cross-sectional area of each of the known gear-type transmission apparatuses viewed in a direction perpendicular to the axial direction of the shafts is widened to include the reverse shaft and the gears supported thereby. Hence, minimization of the known gear-type transmission apparatuses is not sufficient.
A need thus exists to provide a gear-type transmission apparatus which is not susceptible to the drawback mentioned above.